Battery Life and Charge Cycles

Posted on April 3, 2013

There are two camps on how to best protect the capacity of your cell phone battery: charge it when it’s dead, or charge it every night.

I’ve heard older NiCd battery technology should be deep cycled to avoid the old “memory effect”, but our phones, tablets and laptops all have newer lithium-based batteries. The conventional knowledge seems to be that completely discharging a lithium battery permanently degrades its lifespan. But I haven’t found a definitive source on how to best care for my battery.

As an iPhone user, I thought I’d check with Apple first. For maximizing battery lifespan, their website suggests keeping your phone at the right temperature and adjusting your settings to use your battery less. They don’t offer any specific recommendation on deep vs. shallow charge cycling, but they do suggest going through at least one complete charge cycle (charging the battery to 100% and then completely running it down) per month. That seemed like an oddly specific recommendation with no data to back it up.

Checking the Literature

I decided to see what the scientific literature had to say about this. Here’s what I learned:

Measuring Battery Performance: When evaluating any kind of performance, engineers need a metric. The standard lifespan metric seems to be “number of charging cycles through which the battery can retain 80% of its original capacity”. For example, Apple promises 400 charging cycles for your iPhone battery.

Temperature: I found an interesting paper (behind a paywall, unfortunately) on the aging mechanisms of lithium ion batteries. Sure enough, there’s good science verifying that temperature plays a big role in battery lifespan. Most batteries are designed to operate at room temperature, and both hot and cold temperatures accelerate aging. They also note that battery capacity will fade over time regardless of your usage habits because the chemicals simply break down.

Shallow cycling: The best research I could find comparing deep and shallow cycling was Nicholas Williard’s master’s thesis from the University of Maryland. He experimented with a particular make and model of lithium ion batteries. He preconditioned a fraction of these batteries by shallow cycling them 900 times (draining just 7% of charge before recharging). Amazingly, he found the preconditioned (i.e., shallow-cycled) batteries were able to withstand about the same number of deep cycles as brand new batteries. In other words, shallow cycling didn’t seem to degrade battery capacity at all!

My conclusions:

Keep your battery cool (but not cold).
Shallow cycling is OK (go ahead and charge every night… or even more often).
I couldn’t find any research backing up Apple’s “monthly deep cycle” recommendation.

3D Maps Could Lead to Great New Applications

Posted on July 11, 2012

As the world gets ready for both Google and Apple’s competing 3D map services, a lot of people are wondering just why we need 3D maps in the first place. 3D maps are cool and all, but are they game changing? Are they actually useful?

While I haven’t seen any killer 3D map apps yet, the truth is detailed 3D maps of the world’s cities could enable some really cool new applications. Of course, the utility of these mapping services will depend on how much access is given to developers.

The computer vision literature is filled with high-tech algorithms that could exploit a 3D model and mobile camera. For example, “SLAM” (Simultaneous Localization and Mapping) is a break-through algorithm now used frequently in robotics research that allows a robot (or mobile device) to build a 3D map of its surroundings from a video feed and localize itself against this map. It’s not a far stretch of imagination to think that using a 3D map from the web could help solve this problem faster and more accurately. And there other algorithms that match a 2D image to a 3D model.

If mobile developers are able to access the geometries of these 3D models (either as point clouds or meshes), get ready for some truly amazing augmented reality apps. However, if the 3D models are confined in proprietary viewing applications (like Google Earth or Apple’s new map application), I think these 3D maps will quickly lose their novelty.

3D Models, if implemented correctly, could enable new augmented reality applications.

The Steve Jobs Movie

Posted on June 20, 2012

It’s on IMDB, so it must be true: Ashton Kutcher will star in Jobs, a 2013 biopic about the Apple founder. Scrolling through Kutcher’s filmography, I’m going to go ahead and declare that this is his first serious role.

I’m just finishing the biography by Walter Isaacson (I’m late to party, I know), and there’s more than enough intriguing material for a great film. But that’s the problem. As a nerd, I want them to tell a visionary’s amazing success story rather than a cheesy romantic drama.

What the movie should be is an edgy, foul-mouthed drama showcasing the best anecdotes from the book. I want to see Gates and Jobs have at it. I want to see Jobs and Jony Ive look together at a mockup of the first iPhone. And I want to witness freak-outs in full Jobsian narcissistic glory. In short, I want to see the history behind Apple’s products and the computer industry at large. These are the people and events that have shaped my profession and, to a some extent, influenced my life.

But who’s listed third under cast? Ahna O’Reilly playing Chris-Ann Brennan— Jobs’ girlfriend in his twenties and the mother of his first daughter. How is she the third most important “character” in Steve Jobs’ life? This is why tech nerds hate Hollywood.